The present invention relates generally to a dual outlet pyrolyzer used to detect biological agents present in the air.
A chemical biological mass spectrometer block II (CBMSII) detects biological agents present in the air by employing a two step process. During sample collection, a first pump draws 1 liter of air per minute into a pyrolyzer through an inlet. The air drawn into the pyrolyzer includes secondary particles, such as airborne dust, fibers and dirt, and may also include biological agents, such as anthrax spores, bacterium or other particles containing biowarfare agents. A sample of the aerosolized particles is impacted at the bottom of a quartz tube (pyrotube) in the pyrolyzer. The air and residual particles that are not collected in the pyrotube are exhausted through an outlet.
During sample identification, the collected particle sample in the pyrotube is analyzed to identify any biological agents. A small droplet of a methylating reagent, such as tetramethylammonium hydroxide (TMAH) dissolved in methanol, is added to the particle sample in the pyrotube through a hypodermic needle. In one example, the hypodermic needle is made of stainless steel. If the sample includes any biological agents, the methylating reagent derivatizes organic materials to make them more volatile. For example, fatty acids in the cell walls of the bacterial agents form Fatty Acid Methylated Esters (FAMEs).
The sample in the pyrotube is then heated (pyrolyzed) to boil off the FAMES and other low volatile molecular fragments of the biological agents. A second pump draws 1 milliliter per minute of the gas molecules through the outlet and into a mass spectrometer for analysis and identification of any biological agents. Biological agents have a unique mixture of fatty acids and molecular fragments, known as bio-markers. If any biological agents are present in the sample, the mass spectrometer will produce a mass spectrum that indicates mass peaks for each of the bio-markers present. The bio-marker pattern is compared to a pre-programmed list of bio-markers produced by known biological agents to identify the biological agent in the air sample.
The pyrolyzer employs a single outlet line for both the air exhausted from the pyrolyzer during sample collection and the gas molecules directed to the mass spectrometer during sample analysis. The outlet line is a heated, stainless steel tube having a coating (for example, SilcoSteel) that renders the internal walls inert to chemicals.
The volume of gas released during pyrolysis is very small (typically one milliliter). The diameter of the outlet line must be relatively small to minimize the volume and provide fast delivery of the gas molecules to the mass spectrometer.
However, the small diameter (1 millimeter or less) of the outlet line increases the tendency of the outlet line to clog when the air that is exhausted contains a high level of background dust or fiber content.
The inert coating inside the outlet line is effective for transporting the gas molecules formed during pyrolysis, but is not effective in transporting the aerosol particles that are exhausted. The glass like inert coating is an insulator and causes the buildup of static electricity, which causes the aerosolized particles to stick to the inert coating. Over time, particles that coat the inside of the outlet line form chemically active sites that reduce the efficiency of the outlet line to transport the gas molecules to the mass spectrometer. The outlet line can also be periodically flushed with methanol and water to remove the active sites and/or can be replaced monthly. However, this is both laborious and costly.
Additionally, the methylating reagent is strongly basic and can break down the inert coating on the outlet line over time, again reducing the efficiency of the outlet line to transport bio-markers to the mass spectrometer. The outlet line is commonly replaced monthly to prevent this.
The prior art steel hypodermic needle that dispenses the methylating reagent solution also has drawbacks. For one, the needle is not reliable in delivering a consistent metered droplet of the methylating reagent solution, resulting in a lack of repeatability of the experiments. The compression fitting that feeds the needle through the walls of the pyrolyzer conducts heat to the needle, causing the temperature of the needle to increase above the boiling point of methanol and evaporating the methylating reagent solution passing through the needle. Additionally, repeated thermal cycling has been found to “age” the needle. The nickel in the stainless steel alloy can activate the surface and catalyze the break down of the FAMEs during pyrolysis.
Thus, it is desirable to have a dual-outlet pyrolyzer that can more effectively reduce clogging of the outlet line, as well as overcoming the other above-mentioned deficiencies of the prior art.